Egyptian police and protesters clash outside a courtroom in Alexandria, Egypt, on Saturday.

CAIRO — Riot police fired tear gas Saturday to disperse dozens of demonstrators throwing rocks outside an Alexandria courthouse where the city’s ex-security director and other officers are on trial for the killing of protesters during Egypt’s 2011 uprising.

The confrontation comes a week before the country marks the second anniversary of the revolt that ousted the country’s longtime autocratic ruler, Hosni Mubarak, and highlights the frustration expressed by many over the pace of reform in the Arab world’s most populous nation.

Alexandria’s former security director Mohammed Ibrahim is on trial along with five other police officers accused of using excessive violence to put down the 18-day revolt. In Alexandria, as elsewhere in Egypt, thousands of protesters have taken to the streets over the past two years to demand “qisas” — Arabic for retribution — for those killed in clashes with security forces.

Relatives of the dead say they have little confidence in the justice system or police investigations. “It is one long chain of corruption,” said Ramadan Ahmed, whose 16-year-old son Mohammed was shot dead in clashes outside an Alexandria police station.

Since Mubarak was deposed on Feb. 11, 2011, nearly 100 police officers have been brought to trial on charges of killing and wounding protesters, although all were acquitted or received suspended sentences.

Ahmed said he believes the judiciary and the pervasive security forces are still loyal to the former regime.

“No one alive will get their rights until these people who died do,” he said

The Saturday clashes broke out as human rights activists and family members of those killed in Alexandria protested outside the courtroom. Most of their slogans focused on the police but it was not immediately clear how the violence began. At least three demonstrators and three riot police required medical care for tear gas inhalation and injuries from flying rocks, witnesses and state media said.

Later in the day, clashes erupted again after Judge Mohammed Hammad Abdel-Hadi barred the prosecution from calling witnesses to testify.

Out of around 900 people killed nationwide in the anti-Mubarak protests, some 300 were reportedly killed in Alexandria during the revolt. Mubarak and the former interior minister were sentenced to life in prison for failing to stop the killings, and were granted a retrial this month.

Ahmed said the loss of his son still shocks the family and has taken a toll on him.

“Imagine spending 18 years wanting a son and finally having Mohammed,” said the retired naval officer.

Like others who lost loved ones during the uprising, Ahmed said he voted for President Mohammed Morsi, who had been imprisoned under Mubarak for his activities with the then-outlawed Muslim Brotherhood group. Ahmed said he met with Morsi after he was elected last summer in the nation’s first free presidential vote.

“I told him there must be justice for my son. He took the picture of Mohammed and another boy from Suez and kissed it. He asked to keep the pictures and was clearly affected.”

In another case involving protesters, an Egyptian criminal court on Saturday invoked a presidential amnesty and dismissed charges against 379 people accused of taking part in deadly clashes with police.

The charges stem from nearly two weeks of street fighting on downtown Cairo’s Mohammed Mahmoud street in November 2011 that left 42 people dead.

Young protesters, mostly die-hard soccer fans known as Ultras, led demonstrations against police near the Interior Ministry and Tahrir Square, the hub of Cairo’s activist movement. They were demanding a timetable for the military officers who were then ruling the country to hand over power and hold presidential elections.

Since the revolt, security lapses and a weakening of police powers has left many feeling more vulnerable, particularly the country’s Coptic Christian minority.

On Saturday, police said they arrested seven suspected of attacking stores owned by Christians in the southern village of Marashda, in Qena province. Several shops were torched early Friday when word spread that a Christian villager had sexually assaulted a 6-year-old girl. State prosecutors ordered the young girl to be given a physical examination as part of the investigation.